I haven't posted a lot over the past year about what I've been working on, but I've spent a lot of time building a web application that tracks ships around the world using positions relayed by satellite. I'll post more on the project soon, but for now I just want to share one of the ways that we're improving the usefulness of the maps as part of this project.
At their heart, the maps in the application are based on OpenStreetMap data and satellite imagery from MapBox, but when your clients are mostly looking at their vessels in seas and oceans around the world, traditional web mapping data doesn't really give enough context. Marine charts can fill in those big blue gaps and aid with using the map.
MarineFIND - with whom I've been working with to deliver this project - provide marine charts in various formats, including as a tile map service or web map service for clients who are looking to add charts to their own applications. The charts are made available either individually in their original form, or joined together to form an almost seamless detailed chart of the world. The combined chart layer cuts the landmass out, leaving them transparent, allowing the layer to be used on top of satellite imagery or other maps.
Combining two raster datasets - the merged charts and the OpenStreetMap maps - into a single map causes some issues when it comes to labelling. Especially around coastal areas, labels from OpenStreetMap may be obscured when overlaying the marine charts.
This can be overcome to some extent by showing the charts as semi-opaque (see left), but for the satellite data we found another way of doing it (see right). Starting with an unlabelled satellite imagery layer from MapBox (which can be coloured to your liking), we then add the marine charts, and finally a separate MapBox Streets layer showing just line data and labels, meaning that any overlapping labels will be shown on top of the charts as expected.